The present invention relates to a still camera system which is able to selectably load with a film back and a still video back.
There has been disclosed an electronic still camera which takes a still image using a solid-stage image pickup device such as a charge-coupled device (hereinafter referred to as CCD) and then records the still image on a magnetic disk. For example, at pages 80 to 85 of NIKKEI ELECTRONICS issued on July 2, 1984, a Japanese magazine has been introduced such a camera. Minolta Camera Kabushiki Kaisha, the assignee of this invention, has filed a Japanese Utility Model application of No. 36821/1986 relating to a still camera including a camera body to carry alternatively a still video back or a film back. This type of a still camera is constructed in such a manner that a still video back including a solid-state device and an image processing circuit is detachably mounted to a common camera body for carrying a film back. The camera is also constructed in such a manner that, even when loaded with the still video back, the camera remains compact in size and thus, the appearance of the camera is approximately similar to that of a popular single-lens reflex camera. Additionally, when loaded with the film back in place of the still video back, the camera can provide an image formed in the film plane in the same manner as a common single-lens reflex camera.
While a common film camera of a film back type has a display for indicating exposure control modes, a shutter speed, diaphragm aperture value, and a film count number of exposed frames of a film, however, if the still video back is attached thereto, readings including a frame/field recording mode and a track number in place of the film count number should be displayed in addition to the aforesaid readings. It is generally known that such specific information relating to the still video back is displayed on the still video back.
In such an arrangement, both of the displays on the camera body and the still video back should be observed at a time while the still video back is installed, which will cause a problem that a camera operator is required to read the information respectively.
Additionally, the CCD image sensor contained within the still video back is generally 2/3-inch (8.6 mm.times.6.6 mm) or 1/2-inch (6.4 mm.times.4.9 mm) in measurements and smaller as compared to the size of a frame of a 35 mm film (36 mm.times.24 mm). For example, as shown in FIG. 13, when the CCD is 2/3-inch in size, its picture screen 35 on the film plane is 17.6 mm wide by 13.2 mm high at a reducing rate of 1/2 on a relay optical device contained within the still video back. It is possible to provide a picture image exactly on the CCD with the use of a relay optical device which can reduce the size of a 35 mm film screen to that of the CCD, which will be equivalent to filming on the 35 mm frame. However, in this case, such a relay optical device in the still video back becomes greater in size thus to decline the portability when the still video back is attached to the camera body.
Therefore, a system has to be developed to meet the respective screen sizes of the film back and the still video back whichever is installed. In that case, there will be some elements, e.g. an area of measuring light and an area of focus detection, to be varied according to the size of a picture screen. Two resepctive areas of measuring light are shown in FIG. 14-A wherein an area 36 is for a 35 mm film while an area 37 is for the still video back. Similarly, two focus detecting areas are shown in FIG. 14-B wherein an area 38 is for a 35 mm film while an area 39 is for the still video back. Apparently, the light-measuring area and focus detecting area 37, 39 with the still video back installed becomes small in accordance with the size of the CCD. It will be a better idea that a frame display representing the frame of the focus detecting area in the viewfinder is changed in relation to the focus detecting area.
Furthermre, there will be some other elements to be changed and/or modified without relation to the size of a picture screen. For example, the information on film sensitivity required for exposure calculation has to be adjusted to that on equivalent film sensitivity determined by the sensitivity of CCD image sensor, and the restriction of shutter speed and diaphragm aperture value has to be ranged according to the attachment of the film back or the still video back. For a 35 mm film camera, diaphragm aperture ranges from the smallest opening to the greatest opening in an interchangeable lens to be used. When the still video back is installed, the available full opening aperture is limited in size by a diameter of a lens in a relay optical device provided in the still video back. That is, in case that the lens diameter of the relay optical device is smaller than the equivalent to the full-open diaphragm aperture value of the interchangeable lens, the result of calculation will be incorrect when measuring under the full-open diaphragm aperture. Consequently, when the still video back is installed, the available diaphragm aperture ranges from the smallest opening aperture to the interchangeable lens to whichever of the largest opening aperture in the interchangeable lens and the lens in the relay optical device is smaller.
When the shutter is slow, an S/N ratio according to a dark current in the CCD becomes smaller thus to reduce the quality of a picture image to be recorded, which is a specific set-back in CCD. Therefore, the shutter control has to be restricted on the slow side so as not to exceed a certain shutter speed such as 1/2 second or 2 second.
Furthermore, after a back cover of the camera body is opened, so-called initial film loading is carried out by advancing the film automatically until a not-exposed frame of the film is advanced to a photographic position. When the still video back is installed in place of a back cover, the initial loading is not required since erasing and recording on the magnetic disk can be effected automatically and electrically.